Muffle-kiln.



J. B. OWENS.

MUFFLE KILN..

APPLICATION FILED APR.1, 191s.

4 SHEETS-SHEET l.

Patented Deo. 31, 1918..

J. B. OWENS.

MUFFLE KILN.

APPLlcATIoN FILED APR,x.19|B

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I. B. OWENS.

MUFFLE MLN.I

APPLICATION FILED APR. I, i918.

,QSQISQCM Patented Dec. 3l, M18.

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Patented Dec. 31, 1918.

1. BJOWENS.

MUFFLE KILN.

APPLICATION FILED 1m11.191s,

J @Mom/WO1 Ma ML, Grimma? JOHN B. OWENS, OF METUCHEN, NEW JERSEY.

MUFFLE-KILN.

Application led April 1, 1918.' Serial No. 225.926.

annealing of iron, glass, and thel like. The y term ware, 'hereinafter used, 1s intended to include the foregoing enumeration, and all other products, goods, articles, or mat-erial which the kiln is adapted to treat.

My object is to provide improvements in a continuous mulie kiln whereby a variety of regulations of the heat and the paths it may travel, may be attained so that circulation of the heat and the resulting treatment of the ware can Abe varied according to the nat-ure of the voperation being conducted.

Another object is to provide for` the cooling ofthe ware conveying means, suchas the cars usually employed, and the taking oil' of excess heat from the tunnel, independently of the circulation and control of the heat radiated through the muiile Walls into the tunnel.

My improved kiln has muiile walls and.

combustion chambers so constructed and arranged as to lenablef-theheat derived from combustion to bemade available the full length of the .side walls and the crown of the kilnfrorn the fire zone to the entrance end of the" kiln whereby the heat .is radiated into the tunnel containing the ware 40 conveying means in a manner rendering it most effective.

My kiln has a tunnel intol one end of'.

which ware to be burned or-fired is introduced, thence traveling along by means of a suitable conveyer and emerging at the opposite end of the tunnel, as usual in continuous' tunnel kilns. The kiln is, inelect. divided into apreheating zone extending for a certain dist-ance where the ware enters, a burning or firing zone Where the ware is `fully burned or fired, and a cooling zone in which it is cooled before it -is'taken out 'of the exit end of the' tunnel. -both sides of the tunnel 'are combustion 55,chambers which run from the point of vinitial com'bustion to points near the entry end Specification of Letters Patent.

ltongue and groove brick which ma which the draft may be regulate Extending along smaller.

Patented Dec. 31, 1918.

of the kiln. Muiile walls separate the ,combustion chambers from the tunnel. These walls are of novel construction, comprising be of eo any size, the tops and bottoms o which have a tongue and groove, respectively, and being grooved at one end-and tongued at the other. While size is not essential, it is prefv eralble to use 'brick which are eight by 65 twelve inches, or of proportionate dimensions.' The top, bottom, and ends, in such a brick may be about three inches wide, while the remainder of the brick is in the form of a panel. If of refractory material, other than carborundum the panel -portion would be about three-quarters of an inch 'in thickness, but if of carborundum, one-half inch in .thickness will suliice.- These brick or tile are placed on edge with the tongues and grooves interlocking at the tops and ends and sealed along their edges by some suit- 'able material such as soluble glass.` A Inutile wall of this character has great.

strength, small tendency to warp, and per- -v mits a very high degree of heat radiation from the combustion chambers into the tunnel.

At intervals along the length of the combustion chambers there are baffles which sufficiently retard the heat to insure utilization of its full value if such is desired, while v enabling the kiln to be built of relatively short length without decrease in efficiency. i While, in effect, the combustion cham-` 90 bers extend from the point of initial combus-v tion nearly to the entrance end of the kiln, end baffles or partitions are provided beyond the stack take-offs or outlets which divide the combustion chambers into main and sec- 95, ondary ones, the latter beingl opposite the preheating zone'. Dampers control the openings in these end lbaliies and enable the heat derived from combustion to be admitted directly into the secondary combustion chambers, orcut off therefrom. One or more outlets connectl the main combustion chambers with the stack; dempers are (provided by Extending the full length of the burning zone and preheating zone in the crown of the'kiln are'ducts, of whichzthe. central one4 is preferably the largest, the others being Lateral ducts or channels connect the-crown ducts with the combustion chambers on opposite sides of the tunnel. In

'some operations the heat should travel the full length of the crown in the ducts therein, while in other operations it should not flow directly to the entrance end of the kiln in the crown ducts. I provide dampers controlling the crown ducts so that both conditions may be met. Dampers are provided for the transverse or lateral ducts which communicate with the combustion chambers, enabling any desired regulation of the volume and direction of travel of the heat to be obtained.

.In the firing of some products, it is desirable that the heat generated at the point of gas ignition should be taken off in its entirety when it first reaches the stack. In

' other firing operations it may be found depers to be set so that the heat will travel to the entry end of the kiln, then dive down through the lateral ducts into the secondary combustion chambers, thence passing therethrough to the stack. There are return flues leading to the stack from the crown llues' at the entrance end of the kiln, dampers being provided therefor. Heat made to travel to theentry end of the kiln in the crown flues can be caused to dive down into the return fiues and thus be carried back to the stack.

Should the product being treated necessi.

tate it, or the better operation of the kiln require it, .the heat in the main combustion chambers, as well as that in the crown flues, can be carried along through the crown tlues to the entrance end of the kiln and made to dive down the lateral crown lues into the secondary combustion chambers, or, to enter the return flues, and thence pass back to the stack.` To effect this operation, the main stack dampers whichv control the outlets from the main combustion chambers to the stack, may be vpartially or wholly closed.

My novel system of combustion chambers, longitudinal and transverse crown flues, and dampers, permit the heat to rise from the combustion chambers into the crown lues, or, to dive back into the combustion cham bers, or, to pass along the full length of the crown flues, or, only a part of the length of said flues, that is, to the region of the stack.w The kiln is, therefore, adapted for regula! tion enabling it to re or treat various wares and products demanding different temperatures and modes of treatment.

To keep the ware conveying means, such as the cars commonly used, cool when passing through the kiln, I provide air inlet means, subject to damper. control, preferably located under the coolingzone and at a suitable point under the -burning zone and to Vmaintain a semi-inert air vspace' below the car platforms and an air curtain around the edges of said car platforms. At `suitable points, such as in the general region of the stack, flues or ducts are provided which lead from the interior of the tunnel to the stack either by way of a separate trunk flue, or, by connection to the main stack lues from the combustion chambers. These take-off flues preferably open into the tunnel at points just above the car platforms so that the excess heat in the tunnel will be taken off into'the stack, under suitable damper control, and, in connection with the leakage from the semi-inert space below the car platforms, cause a draft which will relieve the tunnel of excess heat and will also maintain the air curtain past the edges of the car platforms,

thus keeping the oar platforms and running gear relatively cool and entirely eliminating ay sand seal which would otherwise be necessary for this purpose. The dampered air inlets into the bottom of the tunnel at the cooling zone and firing zone, described above, are preferably fed by air from cross -tunnels located under the kiln and which may also be used for inspection purposes, enabling an operative to project his head and shoulders through these inlets to view the bottom of the tunnel and under parts of the cars.

I am aware that modifications may be resorted to in carrying out my invention without departing from thev essential principles thereof. The embodiment of the invention hereinafter described and which is shown -in the accompanying drawings is to be considered as illustrative, rather than restrictive of the scope of the invention.

In the accompanying drawings:

Figure 1 is a plan view of .the complete kiln, broken across at severa-l parts;

- Fig. 2, a horizontal section through the same; Fig. 3, a vertical longitudinal section on the line 3-3, Fig. l;

Fig. 4, a cross section on-'the line 4 4, Fig. l;

Fig. 5, a cross section on the line 5-5,

vtra-vel when carrying the ware 5, Figs. -t

admit and discharge cars. Extending crosswise beneath the cooling zone is an inspection and air inlet tunnel 10 provided with suitable steps to enable an operative to enter beneath the tunnel 1. A similar inspection and air inlet tunnel 11 extends beneat-h the burning zone. In the bottom of the tunnel 1 there are provided air inlets 12 and 13 communicating with 'the respective tunnels 10 and 11 for the admission of air to the space 14 below the car platforms 4. Suitable dampers 15 and 16 control the air inlets 12 and 13. These dampers are intended to be set to regularly admit a certain quantity of outside air into the space 14, or, they may be closed at times and opened when it is necessary to admit additional air into the space 1'4. The space 14 constitutes a semiinert airspace in which the running gear of the cars 4 travels. Air leakage past the edges of the car platforms 4 intol the upper space 17 ofthe tunnel constitutes an insulating air curtain around Ithe edges of the car platforms, protecting them against burning from the high temperature in the burning space 17 and the maintenance of the semi-inert airspace 14 below the platforms prevents injury to the running gear of the cars and insures the maintenance of a relatively loW temperature in the space 14. The inlets 12 and 13 are of suflicient size to admit the head and shouldersl of an operative who may thus inspect the semi-inert air space 14 and' determine the condition of the running gear of the cars. To provide the. requisite circulation or air leakage from the semi inert air space 14 into the high temperature or burning space 17 for the maintenance of the air curtain around the edges of the car platforms 4, and 'to take oft' the excess heat radiated into the tunnel. there are provided ducts or flues 18, Fig. 5, which preferably connect with the space 17 as at 19 in the general region of the juncture of the burning zone and preheating zone. These ducts or channels connect with the stack 20 by means of one of the main take-off stack Hues 21 extending beneath the kiln, as shown in Figs. 3l and 5, or a separate flue can connect the iues 18 to the stack 20. Dampers 22 control the take-off iiues 18. T heflues 18 communicate With the space 17 just above the car platforms 4 so that the heat will have accomplished its most effective work on the ware 5 before the excess heat is taken off to the flue 21. The flues 18.provide the requisite'movement of the heat lengthwise of the tunnel in the space 17, in addition to providing a suitable draft to accomplish air leakage from the semi-inert space 14 into the space 17 past the edges of the car platforms. air leakage and draft dispense with the necessity of providing sand seals for the car platforms, but, also, the draft accomplishes Not only does this arrangement of4 movement of the heat in the space 17, along the length of the tunnel, and insuresthe utilization of a high percentage of the heat units.

It will be understood in referring to the movement of the heat in the space 17, that there is no direct combustion within the tunnel 1 and that the heat referred to is that which is radiated through the inutile walls The Inutile walls 23, 23run from the cooling Zone to the entrance end of the kiln and are composed of bricks or tiles of the construction shown in Figs. 8 and 9. The bricks or tiles are relatively thick at their top, bottom and ends, say three inches in a. brick which is eight inches by twelve inches.

.One end has a groove 2-1 and the other end a their joints broken. The tile or brick, eX-

cept at the tops, bottoms and ends are relatively thin, say three-quarters of an inch in thickness in the panel portion 28, for an eight inches by twelve inches size, if made of refractory material other than carborundum; if of carborundum, the thickness need be no more than one-half inch. The Walls thus provided are s upported on the benches or lateral portions 29 of the kiln and thev support the crown 30. Great strength, lightness, and adaptability to freely radiate heat into the tunnel 1 resul'ts from the improved mule wall construction Extending the full length of the burning zone and preheating zone on the opposite sides of the tunnel", and having walls 23 as the inner walls thereof, azre the combustion chambers 31, a portion of which (those parts which are opposite the preheating zone) may be considered as secondary combustion chambers 31a. The remaining lengths of .the combustion chambers, that is, those parts which extend from the cooling zone to the preheating zone, may be 4considered as main combustion chambers. In effect, the combustion chambers run the full length of the kiln, except opposite 'the cooling zone, but as the treatment of different wares or products may require different. paths, and directions ot' travel, for the heat, I preferably provide end baffles 32 having openings 33, Figs. 2 and 5` and controlling dampers 34 by means' of which the secondary combustion chambers 31a may be thrown into communication with the main combustion chambers 31, or, may

be cut oli from direct communication therewith through. the openings 33. The end ballles 32 are located in the region of the stack .20.

At intervals of the length of the main combustion chambers 31 there are provided balles, comprising the overlapping parts 35,

36. arranged in pairs, Fig. 2. The longer baffles project nearly across the combustion chambers 31 from the outer walls 37 of the kiln toward the mullie walls 23. The shorter 1 bellies 36 project from the muille walls 23 toward the outer walls 37 in overlap ed relai .be used invconnection with the kiln.

tion to the baiiles 35, Figs. 2 anc 6. To prevent warping of these bellies by the heat to which they aresubject, they are preferably'lbuilt with inclined faces on the ballies and both bullies 35 and v36 are of general triangular form in cross sectional shape, as shown in Fig. 2.

Any form of heat producing means may burners 38, Figs. 2 and 7, are shown as entering the ends of the combustion chambers through air admission holes 39. The flame and heat derived from the burners 38 travel in the direction of the length of the combustion chambers 31 (and into the secondary combustion chambers 31a, if they are in communication with chambers 31) and is balled or retarded in its travel so that the heat is radiated through the mulie-walls 23 into the space 17. The highest temperaturey 3'5 .A the openings 60'.

u vchambers. 31.- I have shown two main draft i outlets vforeach Amain combustion chamber `31, but one "outlet will suiiice. The outlets 40, 41 communicate with down lues42, 43, Figs. 3 and 5, leading to respective fines or ducts 21 andf44"which conect with thel stack 20. Dampers 45, 46

for the respective outlets 40, 41, enable the draft into the stack 20 from the main combustionl chambers 31 to Abe entirely choked ing to the heat which ma7 be desired. For -.in

down in any desired manner arccordf' stance, if it is desired to surge the *heat-"y from the combustion chambers 31 intothe secondary combustion chambers 31a`through 33, this can be accomplished by suitably choking the opening the damper 34. l,

The secondary combustion chambers 31* are blind at their forward ends, by virtue of Walls or partitions 47, Figs. 2, 3, 4, which provide, 1n connection with the end of the -any desired transverse ducts tothe heat cut oil', fully opened up, or.;V

the circulation and path of travel of outlets 40, 41 andfi rasage() kiln, chambers 48 whose bottoms are in communication with iues 49 which may lead direct to the stack 2O or into one or the other of the cross tlues 21, 44; the latter arrangement is shown. Dampers 50 control the circulation from the chambers 48 to the flues 49.

To obtain the effect of a combustion chamber over the crown 30 and resultant radiation d-own through the crown of the tunnel, to supplement the radiation through the muflle walls, I provide the longitudinal ducts or heat flues 51 and the lateral iues 52 which connect the longitudinal lilies with the combustion chambers 31, 31a on both sidcs'of the tunnel.` To obtain the greatest draft in the center of the crown 30, the central longitudinal ducts or lues 51a may be larger, preferably twice as large as the ccmpanion longitudinal lues 51. The longitudinal fines or ducts 51 are blind at the extreme end 51b of the burning zone and blind at 51C just inward from the entrance 6 of the kiln. These ducts'l or iues run the full length of thel crown 30 as seen in Fig. 1, and they all communicate with the transverse ducts 52. The transverse ducts, where the. open into the respective combustion cham ers 31, 31a on opposite sides of the tunnel, have dampers Y 53, Figs. 1, 4 and 6. These dampers permit be opened, while others areclosed, or any or all of them be shut oil or partially opened, permitting full regulation of the volume or direction of travel of the heat derived from the combustion chambers 31, 31a.

Some operations demand a full supply of heat 'in the ducts 51, 51a, 52 over the preheating zone, while others require that be cut off from, or choked down as it enters, the ducts above the preheating 105 zone. Dampers 54, Fig. 1, control communication between those sections of the longi tudinal ducts 51 51a over the vburning zone and those over the preheating zone, for the foregoing purpose.

The walls of the cooling zone are hollow as shown at 55, Fig. 2, and have ports 56v at their top, Fig. 1. Ports 57, Fig. 3, communicate with the hollow spaces 55 and ad- .mit cooling ,outside air to said spaces, said air rising and voiding through the ports 56,-

as 4proposed in certain of my earlier applica- Operation: The ware on the cars enters at 6 and progresses through the tunnel 1, pass- 120 f'i'ng lfiistfthrough the preheating zone and then the burning zone and cooling zone and out-through the exit 7. The doors 8 and 9 are kept closed except when cars are being introduced or taken out from the tunnel. 4' ,The heat from the combustion chambers 31 '.is always radiated through the muiile walls 23. 1f the dampers 34 are opened and dampers 40, 41 closed, or nearly so, the secondary combustion'chambers 31*l are then in di- 130 rect communication With the chambers 31, and the heat Will surge into the chambers 31a and be directly radiated through the muiile Walls 23 to the goods in the preheating zone. If, however, the dampers 34 are closed and the path of travel of the heat in the ducts 51, 51a over the preheating zone is changed, While there will be direct radiation through the muiiie Walls opposite the secondary combustion chambers 31a, the path of travel .of the heat into said chambers 31.i would not be direct. The arrangement and control of the crown ducts 51, 51a and the provision of the openings 32 and 49 and the dampers 34 and 50 enables the heat to be forced in different Ways in relation to the preheating zone. The provision of the dampers 53 and 54 enables the heat to be made to travel in diiferentvvays in relation to the burning zone.

For instance, in the firing of certain products it may be preferable that the heat generated at the points of gas ignition (near Vthe burners 38) should be taken ofi' in its entirety When it first reaches the stack. Other wares may render it desirable to take the heat Off from the side combustion cham-y bers 31, 31a and not from the crown fines 51, 51a. lues 51, 51a vcan be made to travel the full 'length of the kiln to the entrance end thereof and then caused to dive down through the transverse -flues 52 into the secondary combustion chambers 31"1 and back through the openings 33 and down through the ports 40, 41, back to the stack 20. On the other hand, other products may require the opening of the dampers 34, the surging of the heat along the full length of the combustion chambers 31, 31, the rise of the heat through the transverse flues 52 into the longitudinal 1 -lues 51, 51a, and the travel of the heat along the entire length of the crown 30, the full heat volume being then admitted to the chambers 48 and taken through the fines 49 back to the stack. Again, some of the dampers 53 may be so arranged that the heat Will rise in certain of the filles 52 and travel along the flues 51, 51*L and 'then dive down through other fines 52 and pass again into the combustion chambers.

The foregoing operations Which may be conducted With my kiln are stated as illustrative, `and no-t restrictive, of the draft and heat manipulation possible With the arrangement of combustion chambers, iiues and- For example, the heat in the crovvny Vsides of said tunnel, continuous combustion chambers extending horizontally alongside said muiiie Walls, and upright baiiies arranged at intervals of the length of said,

combustion chambers, adapted to baffle the How of the heat alongside said chambers.

3. A continuousV muiile kiln comprising a tunnel for receiving the Ware or products to be treated, mufiie Walls constituting the sides of said tunnel, combustion chambers extending alongside said muiile Walls, and baffles varranged in overlapping ypairs the members of Which project -part Way across the respective combustion cham'bers from the muffie and outside Walls thereof, said pairs of baiies being arranged at intervals of the length of said combustion chambers.

4. A continuous muiiie kiln comprising a tunnel for receiving the Ware or products to be treated, Inutile Walls pnstituting the sides of said tunnel, and main and secondary combustion chambers extending alongside said muffle Walls which are provided With means for placing them in communication With each other or cutting them off from each other. p

5. A continuous muiiie kiln comprising a tunnel for receiving the Ware or products to be treated, muf'He Walls` constituting the sides of said tunnel, combustion chambers extending alongside said muiiie Walls, controllable draft outlets for'taking off the heat from said combustion chambers, and controllable means located .beyond the draft outlets of extending alongside said muiile Walls,con

trollable draft outlets for takin ofi" the heat from said combustion cham ers, controllable means located beyond the draft outlets of the combustion chambers whereby the combustion chambers may be subdivided into main and secondary chambers which can be placed in communication with each other or shut oii from intercommunication, and baiiies located at intervals of the length of the main combustion chambers.

7. A continuous muiile kiln comprising a tunnel for receiving the Ware or products to be treated, muile Walls constituting the sides of said tunnel, combustion chambers exmunication with the combustion chambers at interv-als of the length thereof, and means for controlling the fiow of heat through said conduits.y

9. A continuous muile kiln comprising a tunnel for receiving the ware or products to be treated, muiiie walls constituting the sides lof said tunnel, combustion chambers extending alongside said Inulie walls, heat conveying conduits extending lengthwlse of the crown of the tunnel which are in communication with the combustion'chambersat intervals of the length of said combustion chambers, and means for controlling communication between different parts of the lengths of said conduits.

10. A continuous muiie kiln comprising a tunnel for receiving the Ware or products to be treated, muflie walls constituting the sides of said tunnel, combustion chambers extending alongside said muile walls, heat conveying conduits extending lengthwise of the crown of the tunnel which are in communication with the combustion chambers, and means for controlling communication between ditl'erent parts of the lengths of said conduits.

11. A continuous mutle kiln comprising a tunnel for receiving the ware or products to be treated, muiile walls consti-tuting the sides of'said tunnel, combustion chambers extending alongside said mufile walls, and a network oi longitudinally and transversely extending communicating heat conveying ducts in the crown of the tunnel, said transversely extending ducts communicating with the combustion chambers at intervals of the length of the latter.

12. A continuous mufiie kiln comprising a tunnel for receiving the ware or products to be treated, mullie walls constituting the sides of said tunnel, combustion chambers extending alongside said muile walls, a net-work of longitudinally and transversely extending communicating heat conveying ducts in the crown of the tunnel, said transversely extending ducts communicating with the combustion chambers at intervals of the length of the latter, and dampers controlling the communication between the transversely extending chiots and the combustion chambers.v

.1.3. A continuous m-uflle kiln comprising a tunnel for recelvlng the ware or products to betreated, muiie walls constituting the Lasaeeo sides of said tunnel, combustion chambers extending alongside said inutile walls, a network of longitudinally and transversely extending communicating heat conveying ducts in the crown of t-he tunnel, said transversely extending duc-ts communicating with the combustion chambers at intervals of the length of the latter, dampers cont-rolling the flow between sections of the longitudinally extending ducts, and other dampers controlling thc communication between transversely extending ducts and the combustion chambers.

14. A continuous inutile kiln comprising a tunnel for receiving the ware or products to be treated, muii'le walls constituting the sides of said tunnel, combustion chambers extending alongside said mufiie walls, means for Subdividing the combustion chambers into sections, longitudinally extending heat-conveyin 'ducts or condu1ts in the crown of the tunne and transverse heat conducting conduits which join the longitud-inal conduits or ducts to the sections of the combustion chambers.

15. A continuous mufie kiln comprising a tunnel for receiving the ware or products to be treated, muiiie walls constituting the sides of said tunnel, combustion chambers extending alongside said muliie walls, means for su'bdividing the combustionchambers into sections, longitudinally extending heat conveying ducts or conduits in the crown of the tunnel, transverse heat conducting conduits which join the longitudinal conduits or ducts to the sections of the combustion chambers, and means for controlling the flow in the ducts 0r conduits in the crown of the tunnel.

16. A continuous Inutile kiln comprising a tunnel for receiving the ware or products to be treated, muilie .walls constituting the Sides of said tunnel, combustion chambers extending alongside said muile walls, means for subdividing the combustion chambers into sections, longitudinally extending heat conveying ducts or conduits in the crown of the tunnel, transverse heat `conducting conduits which Ijoin the longitudinal conduits or ducts to the sections of the combustion chambers, 'and independent draft outlets for the respective sections of the com-l bustion chambers.

17. A continuous muiie kiln comprising a tunnel for receiving the ware or products to be treated, muille walls constituting the sides of said tunnel, combustion chambers extending alongside said muffle walls, means forl subdividing the combustion chambers into sections, longitudinally extending heat conveying ducts or conduits in the crown of the tunnel, transverse heat conducting conduits which join the longitudinal conduits or ducts to the sections of the combustion chambers, independent draft outlets for the respective sections of the combustion chambers, dampers controlling communica-- tion between the', ;t,r,ansverse ducts or conduits and the respective sections of the combustion chambers at intervals of the lengt-hs of the latter, and dampers controlling' communication between different sections of the longitudinally extending ducts or conduits.

18. A continuous muille kiln comprising a tunnel for receiving the ware or products to be treated, muiile walls constituting the sides of said tunnel comprising numerous relatively thin panels with intervening thickened portions throughout the extent of said walls, and combustion chambers outside said mufHe walls.

19. A continuous mufile kiln comprising a tunnel for receiving the ware or products to be treated, muiile walls constituting the sides of said tunnel which consist of brick or tile having interlocking horizontal and vertical marginal portions and substantially uniformly relatively thin panel-like bodies, and combustion chambers extending alongside said mufle Walls.

20. A continuous muiile kiln comprising a tunnel for receiving the ware or products to be treated, muile walls constituting the sides of said tunnel which consist of brick or tile having one of their horizontal edges provided with a tongue and the opposite horizontal edge with a groove and one vertical edge provided with a tongue and the -other vertical edge with a groove, the respective bricksor tiles having their tongues and grooves inter-locked, the bodies of the bricks or tiles being substantially uniformly relatively thin, and combustion chambers extending alongside said mufle walls.

21. A continuous muffle kiln comprising a tunnel for receiving the ware or products to be treated, muflle walls constituting the sides of said tunnel, combustion chambers extending alongside said Inutile walls, ware conveying means for the tunnel Whichsubstantially subdivides said tunnel into an upper section in which the ware is located,

vand a lower section in which the temperature is maintained low enough to prevent injury to the ware conveying means, the said upper and lower sections being sealed from each other except for air leakage from the lower section into the upper section, means for admitting air to the lower section, and means for taking olf heated air from the upper section, whereby a semi-inert air space is maintained below the ware conveying means and heat flow is maintained in the upper section of the tunnel.

22. A continuous mutfle kiln comprising a tunnel for receiving the ware or products to be treated, muile wallsconstituting the sides of said tunnel, combustion chambers extending alongside said muiile walls, said tunnel'having an upper section in which high temperature may be maintained, a lower section containing semi-inert air in which a low temperature may f'be maintained and means permitting air leakage from the lower section into the uppersection, said sections being otherwise sealed from each other. v

23. A continuous muii'le kiln comprising a tunnel for receiving the ware or products to be treated, mule walls constituting the sides of said tunnel, combustion chambers extending alongside said muille walls, said tunnel having an upper section in which high temperature may be maintained, a lower section containing semi-inert air in which a low temperature may be maintained, means permitting air leakage from the lower section into the upper section, said sections being otherwise sealed from each other, and means for taking 0H heated air from the upper section, whereby the semiinert air space is maintained in the lower` section and air circulation is had in said lower section and heat circulation in the upper section.

In testimony whereof, I hereunto aix my signature.

JOHN B. OWENS. 

